/* 进入 */
.title-enter { 
  opacity: 0;
}

/* 进入过程 */
.title-enter-active {
  opacity: 1;
  transition: opacity 1s ease;
}

/* 离开 */
.title-exit {
  opacity: 1;
}

/* 离开过程 */
.title-exit-active {
  opacity: 0;
  transition: opacity 1s ease;
}